From: Linus Torvalds torvalds@linux-foundation.org
commit f66066bc5136f25e36a2daff4896c768f18c211e upstream.
While our user stacks can grow either down (all common architectures) or up (parisc and the ia64 register stack), the initial stack setup when we copy the argument and environment strings to the new stack at execve() time is always done by extending the stack downwards.
But it turns out that in commit 8d7071af8907 ("mm: always expand the stack with the mmap write lock held"), as part of making the stack growing code more robust, 'expand_downwards()' was now made to actually check the vma flags:
if (!(vma->vm_flags & VM_GROWSDOWN)) return -EFAULT;
and that meant that this execve-time stack expansion started failing on parisc, because on that architecture, the stack flags do not contain the VM_GROWSDOWN bit.
At the same time the new check in expand_downwards() is clearly correct, and simplified the callers, so let's not remove it.
The solution is instead to just codify the fact that yes, during execve(), the stack grows down. This not only matches reality, it ends up being particularly simple: we already have special execve-time flags for the stack (VM_STACK_INCOMPLETE_SETUP) and use those flags to avoid page migration during this setup time (see vma_is_temporary_stack() and invalid_migration_vma()).
So just add VM_GROWSDOWN to that set of temporary flags, and now our stack flags automatically match reality, and the parisc stack expansion works again.
Note that the VM_STACK_INCOMPLETE_SETUP bits will be cleared when the stack is finalized, so we only add the extra VM_GROWSDOWN bit on CONFIG_STACK_GROWSUP architectures (ie parisc) rather than adding it in general.
Link: https://lore.kernel.org/all/612eaa53-6904-6e16-67fc-394f4faa0e16@bell.net/ Link: https://lore.kernel.org/all/5fd98a09-4792-1433-752d-029ae3545168@gmx.de/ Fixes: 8d7071af8907 ("mm: always expand the stack with the mmap write lock held") Reported-by: John David Anglin dave.anglin@bell.net Reported-and-tested-by: Helge Deller deller@gmx.de Reported-and-tested-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/mm.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -384,7 +384,7 @@ extern unsigned int kobjsize(const void #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
/* Bits set in the VMA until the stack is in its final location */ -#define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ) +#define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ | VM_STACK_EARLY)
#define TASK_EXEC ((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0)
@@ -406,8 +406,10 @@ extern unsigned int kobjsize(const void
#ifdef CONFIG_STACK_GROWSUP #define VM_STACK VM_GROWSUP +#define VM_STACK_EARLY VM_GROWSDOWN #else #define VM_STACK VM_GROWSDOWN +#define VM_STACK_EARLY 0 #endif
#define VM_STACK_FLAGS (VM_STACK | VM_STACK_DEFAULT_FLAGS | VM_ACCOUNT)